Experiment and Quality Evaluation of Hot-Air Vacuum Combined Drying for Red Jujube Slices Based on Analytic Hierarchy Process

Red jujubes are rich in vitamins and sugar and have high nutritional value, and drying is one of the main ways to process jujubes, extending the shelf life by reducing the moisture content of red jujubes. However, the traditional jujube drying method has problems such as poor quality and low efficiency, and it is difficult to comprehensively evaluate multiple quality indicators in the current analysis of jujube drying, so this paper used the special product of Shaanxi jujube as the test material to study the drying quality of red jujube slices under four drying methods: hot-air drying, vacuum drying, hot-air vacuum combined drying and vacuum freeze drying (reference group), and compared the drying characteristics of them. Drying time, rehydration ratio, color difference, Vc content and texture characteristics were used as evaluation indexes, and the analytic hierarchy process (AHP) was used to comprehensively score hot air drying, vacuum drying and hot air vacuum drying. The experimental results showed that the drying of red jujube slices was controlled by both external water evaporation and internal water diffusion. The effective moisture diffusion coefficient D_eff of hot air drying was the largest, followed by hot air vacuum combined drying, and the effective moisture diffusion coefficient of vacuum drying was the smallest. In terms of drying quality, vacuum freeze drying (reference group) has the best quality in terms of Vc content, color difference, and rehydration ratio, but its high drying time increases its energy consumption and drying cost. However, we used the AHP to rank the overall scoring of hot air drying, vacuum drying and hot air vacuum drying, and the highest overall scoring was hot air vacuum combination drying.